Apparatus for coating incandescent



APrll 13, 1954 L. THORINGTON APPARATUS FOR COATING INCANDESCENT LAMPS WITH A DIFFUSING COATING Filed Jan. 30, 1951 A 0K5 WWW/V670 g2 ATTORN EY Patented Apr. 13, 1954 APPARATUS son COATING INCANDESCENT LAMPS WITH A DIFFUSING COATING Luke Thorington; Glen Gardner, N. .L; assignor to Westinghouse Electric Corporation East Pittsburgh, Pa., a corporation of Pennsylvania Application January 30, 19h, Serial as. 208,572

9 Claims.

have been a separate diffusing surface associated with the bulb of an incandescent lamp, inside frosting or etching the bulb, a superficial coating of a preparation, such as an enamel or the like, to the bulb of the lamp, and inside coating or" the bulb with fine particles of silicon dioxide.

The last-named method is the most recent and apparently capable of the best results. The silica used must be of high quality and desirably has a final coating particle size corresponding in diameter with the wavelength of visible light, 1. e., approximately 5060 A. U. or 0.5 micron. A number of methods for coating the bulb of an incandescent lamp with fine particles of silicon dioxide have been used, such as liquid: flush. coating, electrostatic coating, and coating by burning any of a number of organic silicon compounds to remove the organic components and deposit silicon dioxide smoke on the bulbs.

Of the organic silicon compounds employed, ethyl silicate appears to give" best overall results;

although the burning tip requires continual cleaning to avoid clogging. In addition, the attendant hazard of an explosion lessens the inherent value of this coating method.

Further, in all of the above mentioned coating methods, lack of proper control of the uniformity of resultant particle size of coating on the bulb is a serious defect. The coating equipment used in each case is complicated and expensive. Such equipment in each respective case is not readily combined in a production line with the sealing and exhaust operations on one automatic machine.

Hence, it has been found advantageous, according to my invention, to employ the method of coating the bulb with a diffusing medium. by subliming a less pure grade'of amorphous silica onto the bulb to be coated. The method consists of heating the silica or silicon dioxide within the bulb before sealing a mount therein to convert the silica from a solidto avapor and coridense the silica vapor on the bulb as by cooling until the desired surface brightness or coating density is obtained.-

One method of subliming the silicaonce the bulb comprises mounting a small tungsten filament within a small open-ended refractory container, packing. the silica powder around the filament, and heating the silica.

A second method for purifying and at the same time subliming the silica onto the bulb comprises the use of two carbon electrodes having axial holes packed with silica powder, and heating the silica by an electric are between said electrodes.

A third method for subliming the silica onto the bulb' comprises mounting two small diameter carbon electrodes projecting into a small openended refractory container in which the silica powder is packed and heating the silica by an electric are between said electrodes.

In its general aspect, the present invention has as its objective the elimination of the disadvantages and defects of the prior art coating of incandescent lamp bulbs with a diffusing medium.

Another object of the present invention is the coating of an incandescent lamp bulb with a diffusing medium by equipment of the utmost simplicity.

Further, an object of the present invention is the use of a less pure grade of silica in the coating of an incandescent lamp bulb with a diffusing medium".

A still further object of the present invention is the coating of an incandescent lamp bulb with a diffusing medium by equipment having close automatic control.

Another object of the present invention is the coating of an incandescent lamp bulb with a diffusing medium of extremely uniform particle size.

A further and general object of the present invention is the coating of an incandescent lamp bulb by subliming a diffusing medium onto the bulb.

A still further and specific object of the present invention is the use of apparatus for coating a bulb with a diffusing medium, comprising silica packed about a tungsten filament within a refractory' open-ended container.

An additional object of the present invention is theuseof apparatusfor coating a bulb with a diffusing medium, comprising silica packed within the axial holes of two carbon electrodes.

A still further object of the present invention isthe useof apparatus for coating a bulb with a diffusing medium, comprising a refractory open-ended container and packed silica between two small carbon electrodes within said contimer. 7 p

cbj ect's' of the invention will appear to those skilled in the art to which it appertains as the description thereof proceeds, both by direct recitation thereof and by implication from the context.

Referring to the accompanying drawing in which like numerals of reference indicate similar parts throughout the several views:

Fig. l is an elevational view of an incandescent lamp with a part broken away to show the diffusing medium on the inner surface of the envelope;

Fig. 2 is a sectional view of a lamp envelope, showing a refractory container having silica packed about a filament therein;

Fig. 3 is a sectional view of a-lamp envelope, showing two carbon electrodes having silica packed in axial holes therein;

Fig. 4 is a sectional view of a lamp envelope, showing a refrectory container having silica packed about two carbon electrodes therein.

In Fig. 1, the reference numeral ||l designates thebulbouslvitreous envelope of an incandescent electric lamp. The inside surface of said envelope is'coated, as hereinafter explained, with a layer of silica ll of controlled density, as the diffusing mediurrri Suitably sealed to the neck of envelope I is a filament mount l2, comprising a suitable stem I3, filament I4, and filament support wire 15. Attached to the lower extremity of the neck of said. envelope is a base 9.

In Fig. 2, wherein the apparatus for coating the envelope ID with thedifiusing medium by a preferred method is shown, envelope in is juxtaposed suitably axially about the coating apparatus l6. Said apparatus. 6 comprises a refractory ceramic open ended container l1, hollow mounting rod I8, heating filament l9, silica 2D, filament lead-in -conductors 2|, suitably insulated from each other, and'coating density control apparatus 22. Said container 1 has a threaded stud 23 of refractory metal axially joined by a suitable threaded connection to the'outer surface ofthe bottom of container l1. Also projecting from said bottom and joined thereto, also by threaded connections, are hollow refractory pipe-like nipples 24Withappropriate set screws 25 threaded through thesidewall of each for securing the legs of filament H! in any desired position.

The rod I8 is handily threaded on its upper end to receive stud23, thereby securing container inplace. Two holes 26. through the side wall of rod l8 rear its upper threaded end permit passage of leading-in conductors 2| from the legs of filament 19, where said conductors .are secured, as by welding, throughsaid side wall .and down rod l8 to apparatus 22 and the line voltage sup.- ply 21. Silica 2|]v is packed about the filament l9 to a convenient depth within container 1. Such silica neednot be of such high ,qualityas is normally used in the art.

Automaticclose control of the coating density of the diffusing medium is achieved by apparatus 22 which comprises a photocell or similar light sensitive element28, an amplifier and relay circuit 32 for energizing an electromagnet 33, switch 34, and normally closed contact 35.

The source of power 21 connects through switch 34 and lines 36 and 31 to the amplifier and relay circuit 32, said circuit being, in turn, connected through lines 38 and 39 and 4t and 4|, respectively, to photocell 28 and magnet 33. The source 21 also connectsto lead-in conductors 2| through lines 42 and 43, the former through contact 35.

The electromagnet 33 is suitably disposed in close proximity tospring loaded (not shown) magnetic contact 35, so that said contact may be opened by the magnet when it is energized.

It will be understood that silica vapor would always surround the heating filament l9 by the time said filament reaches operating temperature, thus protecting the filament from oxidation during operation. Therefore, the use of a protective atmosphere during coating operation may be optional. When a protective atmosphere is employed, hollow mounting rod I8 is suitably vacuum-sealed at its lower end, as by brazing, to metallic cap 46. Appropriate holes are drilled through the bottom of cap 43 to permit passage of the insulated. lead-in conductors 2| therethrough. A suitable enamel painted over the holes and conductors at the point of emergence of said conductors from the cap 46 completes the seal.

In turn, the rod 8 is coaxially and hermetically joined as by brazin along the side walls of a suitable hole in a flat metallic mounting plate 41 having legs or other supporting means 48. Attached to plate 4! in a vacuum-tight joint, through an appropriate hole therethrough, is an exhaust pipe 49. This pipe 49 connects through a T connection 50 to a valve 5| and a suitable pump (not shown) on one side of connection 53 and to valve 52 and the atmosphere on the other sideof connection 50. To complete the protective system, the open-end of envelope i8 is supported on a washer-like rubber gasket 53 located axially on the upper surface of plate 4?.

In Fig. 3, an apparatus for coating the envelope Hla with the difiusing medium by an alternative method of the invention is shown. In this modification, envelope Illa suitably axially situated over two axially hollow carbon electrodes or tubes 54, handily disposed with respect to each other for the generation of an electric arc discharge when an appropriate voltage from source 21 is applied through control apparatus 22 (Fig. 2) between the electrodes 54. Into the axial cavity of each electrode 54 is packed silica 200..

Fig. 4 shows an apparatus for coating the envelope lfib with th diffusing medium by another method of my invention. Envelope liib is axially arranged about coating apparatus 55. Such apparatus 55 comprises an open-ended refractory ceramic container llb suitably secured by threaded stud 23b to the threaded end of hollow mounting rod l8b, two small solid carbon electrodes 55 each with a refractory metal connector 5?, silica 20b,ilead-in conductors 2| h and the control apparatus 22 as shown in Fig. 2. The electrodes 56 project interiorly through suitable holes in the side wall of container Ill) and are covered to a suitable depth with finely divided silica 2th, withincontainer Ill). The outer extremity of each electrode is secured in a suitable hole in one end of eonnectoril by a set screw 53. In turn, the other end of said connectors is joined as by welding to the lead-in conductors 2 lb.

According to my invention, the envelope |iJ,,to be coated with a diffusing medium by the preferred embodiment of coating apparatus as shown in Fig. 2, is axially aligned over a coating apparatus it. By closing switch 34, line voltage, suitably volts A. 0., from source 27 heats filament l9 of the coating apparatus VI 6 above 1750 C. Vaporized silica 29 from container l'i condenses uniformly on the cooler surrounding envelope It to produce the desired coating density, as measured by the diffuse light intensityfrom filament l9. When the desired light intensity is received through the coating by photocell28, it actuates 5 amplifier and relay circuit at to energize electromagnet 33. In turn, magnet 33 moves normally closed contact 35, thereby opening supply line 42 and shutting off power to the filament it.

If a protective atmosphere is employed during the coating process, envelop isaxiall'y aligned with respect to coating apparatus i and the open end of the envelope is supported on rubber gasket 53. Valve 52 to the atmosphere is closed and valve 56 to the pumping means is opened. When the desired degree of vacuum is obtained, envelope I0 is coated with "the diffusing medium upon closure of switch 34, as explained above, in the protective vacuum.

To remove the coated envelope I'D, the pumping means is shut off through valve El and air at room pressures admitted through valve 52, thereby breaking the seal between the open end of coated envelope [0 and gasket 53 and allowing removal of said coated envelope in. I

It will be understood that the protective atm'osphere used in coating the envelope may also be an inert gas, such as nitrogen, argon, or the like.

According to my invention, envelope Illa may i also be coated with a diffusing medium by an alternative embodiment of the coating apparatus shown in Fig. 3. Said envelope is centered longitudinally over the two axially hollow carbon electrodes 5 which are packed with silica 28a. Line voltage applied through switch 34 and coating density control apparatus 22 (Fig. 2) initiates an instantaneous are discharge between electrodes 54. At temperatures well above 1750 C. the silica a in the axial cavities of electrodes 54 sublimes onto the inner surface of envelope Illa. When a sufficient coating density is achieved, the resultant intensity of light causes the electromagnet 33 to open contact and extinguish the are between the electrodes 54.

Further, according to my invention, the envelope Hlb may be coated with sublimed silica Hb, as a diffusing medium by the coating apparatus of Fig. 4. After centrally locating the envelope Hlb, about the coating apparatus 55, and applying line voltage to the density control apparatus 22 and across the two small solid carbon electrodes 56, an arc discharge is initiated therebetween. The are discharge continues to sublime the silica 28b onto the inner surface of en velope 10b at temperatures in excess of 1750 C. until the desired coating density is obtained and the arc is terminated by the energization of magnet 33 and the opening of contact 35 in the same manner as previously explained relative to Figs. 2 and 3.

It will be seen from the foregoing, that my invention achieves the coating of a diflusing meduim on the envelope of an incandescent lamp with coating equipment of the utmost simplicity. By subliming the silica powder 20 onto the envelope l0, according to my invention, I am able to employ less pure silica than used in conventional methods and to purify the silica 20 by the sublimation itself. Through the use of coating density control apparatus 22, I am able to closely control the coating density of the sublimed silica on the envelope l0 and, at the same time, obtain extremely uniform particle size.

Specifically, the preferred method of my invention for subliming silica onto the envelope i0 consists of heating above 1750 C., silica 20 packed about a tungsten heating filament [9 within an open-ended refractory ceramic container IT by applying line voltage to said filament 19. An alternative method of my invention comprises heating above 1750" C. the silica 20a packed in the axial holes of two carbon electrodes 54 by an electric are between said electrodes and subliming said silica onto the "envelope Illa. A further alternative method of myinvention sublimes the finely divided silica 20b onto the envelope Nib by vaporizing said silica from a refractory open-ended container 11h by an electric are between two small solid harb'on electrodes 56 within said container lib and condensing said silica on the envelo e Nib.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

I claim:

1. Apparatus for coating the inner surface of an envelope for an incandescent lamp with sublimed finely divided silica as a diffusing medium, comprising means disposable within said envelope for containing silica, and heating means for raising the temperature of said container above 1750 C., and a coating density control apparatus in electrical parallel with said heating means and having photoelectric means for automatically shutting off said heating means when the desired coating density is obtained.

2. Apparatus for coating the inner surface of an envelope for an incandescent lamp with sublimed finely divided silica as 'a diffusing medium, comprising; means disposable within said envelope and having an open-ended refractory container for silica and a heater filament in said container for raising the temperature of said container above 1750 C., and a coating density control apparatus adjacent said envelope in e1ectrical parallel with said filament and having photoelectric means for automatically shutting off said filament when the desired coating density is obtained.

3. Apparatus for coating the inner sur'face of an envelope for an incandescent lamp with sublimed finely divided silica as a diifus'ing medium, comprising; means disposable within said envelope and having a refractory open-ended container for silica and a heater filament in said container for raising the temperature of said container above 1750 C. and a protective atmosphere also within said envelope; and a coating density control apparatus having photoelectric means adjacent said envelope, in electrical parallel with said filament and which automatically shut off said filament when the desired coating density is obtained; and a protective atmosphere also within said envelope.

4. Apparatus for coating the inner surface of an envelope for an incandescent lamp with sublimed finely divided silica as a diffusing medium comprising: means disposable within said onvelope and having two carbon electrodes provided with axial holes for silica and an electric discharge are between said electrodes for raising the temperature of said electrodes above 1750 C.; and a coating density control apparatus adjacent said envelope, in electrical parallel with said electrodes and having photoelectric means which automatically shut off said are when the desired coating density is obtained.

5. Apparatus for coating the inner surface of an envelope for an incandescent lamp with a sublimed finely divided silica as a diffusing medium comprising: means disposable within said envelope and having a refractory open-ended container for silica, two carbon electrodes in said container and an electric arc discharge between said electrodes for raising the temperature of said container above 1750 C. and a coating density control apparatus adjacent said envelope, in electrical parallel with said electrodes and having photoelectric means which automatically shut ofi said are when the desired coating density is obtained.

6. Apparatus for coating the inner surface of an envelope for an incandescent lamp bulb with sublimed finely divided silica as a diiiusing medium comprising: means disposable within said envelope and having an open-ended refractory container for silica, a heater filament in said container for raising the temperature of said container above 17 50 C. and a protective atmosphere also within said envelope; and a coating density control apparatus adjacent said envelope and having a light-sensitive element and an amplifier and relay circuit in electrical parallel with said filament for energizing an electromagnet and automatically opening a normally closed contact in one side of a filament voltage line when the desired coating density is obtained.

7. Apparatus for coating the inner surface of an envelope for an incandescent lamp with sublimed finely divided silica as a diffusing medium comprising: means disposable within said envelope and having two carbon electrodes provided with axial holes for silica and an electric discharge arc between said electrodes for raising the temperature of said electrodes above 1750' C. and a coating density control apparatus adjacent said envelope and having a light-sensitive element and an amplifier and relay circuit in electrical parallel with said electrodes for energizing an electromagnet and automatically opening a normally closed contact in one side of a filament voltage line when the desired coating density is obtained.

8. Apparatus for coating the inner surface of an envelope for an incandescent lamp with sublimed finely divided silica as a diffusing medium comprising: means disposable within said envelope and having within an open-ended refractory container for silica, two carbon electrodes in said container and an electric arc discharge between said electrodes for raising the temperature of said container above 1750 C.; and a coating density control apparatus adjacent said envelope and having a light-sensitive element and an amplifier and relay circuit in electrical parallel with said electrodes for energizing an electromagnet and automatically opening a normally closed contact in one side of a filament voltage line when the desired coating density is obtained.

9. Apparatus for coating the interior surface of an envelope for an incandescent lamp with sublimed finely divided silica as a diffusing medium, comprising an open ended refractory container for silica within said envelope and havinga heater filament therein for raising the temperature of said container above 1750 0., said heater filament having input leads and a normally closed contact in one of said leads, a protective atmosphere also within said envelope. and a coating density control apparatus adjacent said envelope and having a light sensitive element in contiguous relationship with the portion of said envelope to be coated and an amplifier and relay circuit in electrical parallel with said filament leads for energizing an electrode magnet in operable proximity to said contact for automatically opening said contact when the desired coating density is obtained.

'ieferences Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,164,332 Macksoud July 4, 1939 2,237,328 Birdseye et a1. Apr. 8, 1941 2,338,234 Dimmick Jan. 4, 1944 2,386,875 Morgan Oct. 16, 1945 2,456,708 Kellogg Dec. 21, 1948 2,465,713 Dimmick Mar. 29, 1949 2,545,576 Godley Mar. 20, 1951 

